First principle study of anomalous Hall effect and orbital magnetization in non-collinear antiferromagnets Mn3X (X=Rh, Ir, Pt, Ga, Ge, Sn)

• Main Authors: Tzu-Cheng Wang, 王子政
• Other Authors: Guang-Yu Guo
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/bnq8tq

碩士 === 國立臺灣大學 === 物理學研究所 === 105 === The anomalous Hall effect (AHE) can be considered as a kind of Hall effect without external magnetic field. It has been thought to be present only in ferromagnetic conductors, with its size being proportional to the net magnetization. Using the Berry phase concept and first principle calculations, physicists recently demonstrated that large AHE may appear in noncollinear antiferromagnets, which is driven by the non-vanishing Berry curvature because of the symmetry breaking of their magnetic configuration and spin-orbit coupling. While the spintronics are becoming promising, the understanding of the antiferromagnets are of interest for its development. In this thesis, we study the electronic and magnetic structure of the noncollinear antiferromagnets Mn3X (X=Ga, Ge, Sn, Ir, Rh, Pt) by first principles density functional theory calculations. At broken-symmetry direction, the anomalous Hall conductivity is about 100 to 300 (S/cm), which has the same order as the normal ferromagnetic iron. We also study their orbital magnetization by modern theory of orbital magnetization. The magnitude of orbital magnetization in Mn3Rh, Mn3Ir and Mn3Pt is equivalent to spin magnetization. As for Mn3Ga, Mn3Ge and Mn3Sn, their orbital magnetization is even larger than spin magnetization. The results could explain that the weak ferromagnetism observed in experiments, is caused by the orbital contribution, instead of the spin contribution that dominates the magnetization in most of the magnetic system.